Map information used in a map information system (GIS) and the like is provided in a format managed by mesh and layer. In general, map information becomes obsolete as a time passes because planimetric features (buildings, roads, rail roads, and the like) are newly constructed, broken and removed, and modified, or a landform is changed by construction and a natural phenomenon. Accordingly, it is necessary to periodically update the map information. In many cases, the map information is updated using a map information distribution system.
A map information distribution system disclosed in Patent Document 1 is known as a conventional map information distribution system. FIG. 10 is a view showing an overall arrangement of the map information distribution system disclosed in Patent Document 1. The map information distribution system is arranged by connecting a map information management system 100, which updates, manages, and distributes map information, to a server 105 of a destination, which is located in the destination of map information, and to an information communication terminal 106 of the destination through a network 104.
The map information management system 100 is composed of a transmission system 101 and a reception system 102 which are connected to each other through a communication line 103. Further, the server 105 of the destination and the information communication terminal 106 of the destination are connected to the transmission system 101 through the network 104.
The transmission system 101 is a system which is installed on a vender side of the map information and transmits the map information to the reception system 102. The transmission system 101 has a communication apparatus 110, a host computer 111, and a database 112.
The database 112 stores the map information to be distributed to a buyer. The database 112 is composed of a space database and a cache information database. The space database stores configuration data and attribute data as a table. The configuration data is data showing the configurations of an object (planimetric features such as roads, structures, and the like) constituting a map. The attribute data is data showing the attribute of the object (name and the like of planimetric features). The cache information database stores the drawn data of digital map information divided into a plurality of regions so that the drawn data can be updated in a unit of tile using each region, which is a unit of division, as the tile.
In contrast, the reception system 102 is installed on the buyer side of the map information, receives the map information data distributed from the transmission system 101, and updates the map information thereof. The reception system 102 has a communication apparatus 120, a host computer 121, and a database 122.
The database 122 is a database in which the map information held by the reception system 102 is stored. The database 122 is also composed of a space database and a cache information database likewise the database 112.
In the map information distribution system, the map information is distributed as described below.
First, it is assumed that the difference update information of the attribute data and the configuration data is sent from the server 105 of the destination and the information communication terminal 106 of the destination to the transmission system 101 through the network 104 after it is related to objects. The transmission system 101 updates the attribute data and the space data of the object, to which the space database in the database 112 corresponds, based on the received difference update information. The drawn data of the digital map is created based on the configuration data after it is updated.
Next, the transmission system 101 extracts the tile of the drawn data (hereinafter, referred to as “tile to be updated”) which is changed by the difference update information. The transmission system 101 updates the drawn data of the tile to be updated of the cache information database in the database 112 based on the drawn data of the extracted tile to be updated.
The transmission system 101 periodically distributes the drawn data of the extracted tile to be updated and the attribute data of the changed object (hereinafter, referred to as “object to be updated”) as differential data to the reception system 102 through the communication line 103.
When the differential data is distributed from the transmission system 101 to the reception system 102, the reception system 102 updates the drawn data of the tile to be updated of the cache information database in the database 122 based on the drawn data of the tile to be updated included in the differential data. Further, the reception system 102 updates the attribute data of the object to be updated of the space database in the database 122 based on the attribute data of the object to be updated included in the differential data.
Here, the update information of the map information, which is distributed from the vender to the buyer, is arranged as differential data. This is because since the ratio of the data amount of update information, which occupies the data amount the overall map information, is small, it is not effective to replace the overall map information each time map information is updated and a time and a cost necessary to distribution is wasted thereby. A method of creating the differential data is disclosed in, for example, Patent Document 2.
In the method of creating the differential data disclosed in Patent Document 2, first, a difference between a map before it is updated (hereinafter, referred to as “map before update”) as a reference map and the latest map (hereinafter, referred to as “map after update”) is determined on a transmit side (transmission system 101). With this operation, difference information composed of only the data of updated roads and landmarks is created.
FIGS. 11 (a), 11(b), and 11(c) show examples of difference information. FIG. 11(b) is a map before update, and FIG. 11(c) is a map after update. The difference information shown in FIG. 11(a) is created by obtaining the difference between the two maps. A data transfer amount can be reduced by distributing the difference information, thereby an update process can be suppressed to a minimum necessary amount.
Further, in general, map information has a different format depending on a buyer. Accordingly, when the transmission system distributes updated map information, it must distribute the updated map information after the format thereof is converted into a format of each buyer. Further, it is also possible to apply a method disclosed in Patent Document 3 as a technology related to format conversion. In the method disclosed in Patent Document 3, when updated map information is distributed, a conversion program, which is different to each buyer, is distributed together with map information created by a common format. Then, the reception system converts the data of the common format into data of an original format.
Further, when a part of a map before update is updated, a matching process must be performed between an updated portion and a not-updated portion.
The “matching process” means a process for extracting the portion of map information (hereinafter, referred to as “related information”), which is other than an updated portion of the map information (hereinafter, referred to as “updated information”) and conflicts with the updated portion of the map information and additionally updating the extracted portion of the map information so that the related information does not conflict with the updated information. A method of automatically performing the matching process is disclosed in Patent Document 2.
When, for example, the attribute of a link is changed, the update link may extend over a plurality of tiles. It is assumed, for example, that the update link extends over a tile A and a tile B. In this case, when only the link of the tile A is updated, the attribute of the link of the tile A is not matched with that of the link of the tile B. Accordingly, in the matching process, the link in the tile B that corresponds to the updated link in the tile A is also updated.
In the transmission system, when the map information is updated the distribution of the updated map information, the above matching process must be performed before updated map information is transmitted. An apparatus for automatically performing the matching process before transmission is disclosed in Patent Document 2.
Patent Document 1
    Japanese Unexamined Patent Application Publication No. 2005-258340Patent Document 2    Japanese Patent No. 3391171Patent Document 3    Japanese Unexamined Patent Application Publication No. 11-258981